The present invention relates to gas turbines. It further refers to a gas turbine with a diffuser.
In gas turbines, especially those for combined cycle applications, the exhaust gas temperatures are so high that the support structure of the exhaust duct is no longer allowed to come into contact with the exhaust gas. Thus, the support structure of the exhaust duct has to be protected by means of an insulation, which then has to be covered and protected by liner segments. Exhaust ducts and diffusers of that kind are for example disclosed in documents U.S. Pat. No. 5,104,286 A, U.S. Pat. No. 5,669,812 A and U.S. Pat. No. 6,807,803 B2.
FIG. 1 shows the principle configuration of an exhaust section of such a gas turbine. The exhaust gases emerging from the gas turbine 10 are expanded in a conical diffuser 11 and then enter an exhaust duct 12, which leads the exhaust flow 18 to a stack 19, not shown. The diffuser 11 comprises an inner cone 13 and an outer cone 14, which are coaxially arranged with respect to a machine axis 34. The walls of the inner cone 13 and outer cone 14 and exhaust duct 12 each have an internal structure comprising a liner 15, an intermediate insulation 16 and a support structure 17. Depending on the specific configuration the inner and outer cone 13, 14 can also be cylindrical.
The fixation of the liners is difficult due to several problems:                as the support structure is cold and the liner is hot, there are different thermal expansions, which have to be safely absorbed by the fixtures or fixing means;        the fixtures cross the insulation, thereby creating thermal bridges;        the side of the liner exposed to the exhaust flow must be as flat as possible to avoid disturbing the flow and creating turbulent flow; as the liner has to be mounted somehow, this is hard to achieve;        longitudinal ribs extending into the flow are tolerable for some parts with not too high flowing velocity; however, they cannot be tolerated in the diffuser section, as in this section there may be still an exhaust gas swirl and longitudinal ribs may reduce the diffuser efficiency; therefore, an aim should be to have a smooth surface of the liner at its exhaust flow side, especially in the diffuser section.        
FIG. 2 shows an exemplary prior art solution, where the wall comprises a support structure 21, an intermediate insulation and a liner 23, which is fixed by means of U profiles 24 and threaded joints 25, which disadvantageously extend into the exhaust flow.
Experience has further shown that the nuts, which are secured to the threaded bolts by means of welding points, break off, thereby putting the fixation at risk.